The present invention relates to pumps in general, and more particularly to pendular piston pumps.
There are already known various constructions of pumps for pumping liquids or gases, among them such using a pendular piston, that is, a piston which carries out a pendular movement as it reciprocates in its cylinder bore. In the known pumps, it is customary to use sealing means for sealing the piston in its associated cylinder bore, so as to sealingly separate a pumping chamber from the remainder of the internal space of the housing of the pump. Such sealing means may include a substantially cup-shaped or dish-shaped sealing element which includes a substantially radially extending support section or region at least partially supported on the piston, and a lip section or region which extends from the support region and sealingly contacts the internal surface of the pump housing within the cylinder bore.
In pumps or compressors of conventional construction the plunger piston and the connecting rod acting thereon so as to move the piston to and fro in the axial direction of the cylinder bore are constructed as two separate parts which are connected with one another by means of a piston bolt. What is disadvantageous in this conventional construction is that the piston bolt and the lubricating arrangement needed for lubricating the same are situated at a relatively hot zone of the pump. From this, there result, among others, problems with respect to the lifespan of the lubricant for the lubrication of the piston bolt. Furthermore, lateral guidance forces come into existence between the aforementioned plunger piston and the internal surface of the housing that bounds the cylinder bore for the piston, so that usually guidance rings are required for the piston Such piston rings constitute parts which are subjected to a significant amount of wear.
In order to avoid these disadvantages of the conventional pumps employing a plunger piston, there have been already developed so-called pendular piston pumps. In such pumps, the piston proper and the connecting rod therefor are of one piece and constitute a piston member. Because of the resulting rigidity of the piston member, that is, the absence of the articulate connection between the connecting rod and the piston proper, the piston shares the pendular movement of the piston rod as the latter is being moved by a crank drive, while the piston simultaneously reciprocates in the cylinder bore of the housing. A particular danger encountered in connection with such pendular piston pumps is the possibility of leakage of the medium being pumped past the piston, owing to the tilting movement of the piston with the connecting rod. This danger is especially pronounced at and around the central position of the piston within its stroke, that is, intermediate the two axially spaced reversing positions, where the piston is inclined or tilted the greatest extent relative to the longitudinal axis of the cylinder bore. In heretofore proposed pendular pistons (see, for instance, U.S. Pat. No. 3,961,869), this potential drawback is at least substantially avoided by providing the pendular piston with an annular substantially cup-shaped or dish-shaped seal.
However, even such pumps possess significant drawbacks. Usually, the annular seal of the prior art is punched out of elastic or deformable plates (often Teflon plates). Hence, the annular seal has the same wall thickness at its lip region which contacts the internal surface of the housing within the cylinder bore as at its support region which extends substantially radially outwardly from the piston and is at least partially mounted on the latter. As a result of this configuration, the known sealing elements do not offer a sufficient resistance to be able to laterally support the piston in the associated cylinder bore. Moreover, at least theoretically, the pressure of the medium being pumped, such as gas, does not exert any lateral guidance forces on the pendular piston, in that such pressure always acts in the direction of the axis of the connecting rod of the pendular piston member. Yet, in practice, at least some lateral guidance forces, albeit minute, still exist in the environment of the conventionally constructed pendular piston. Such small lateral guidance forces are caused primarily by friction and inertia.
It will be appreciated that the non-existent or insufficient lateral guidance and support of the pendular piston member in the associated cylinder bore results in premature or excessive wear of the lip region of the annular seal. Also, there exists the danger that, because of the thinning of the lip region as a result of the wear of the latter, the "lower" piston part which is situated "downwardly of" the sealing element could come into contact with the surface bounding the cylinder bore and and cause damage thereto. It is to be understood that expressions such as "lower" or "downwardly of" are being used herein, to means closer to the crankcase of the pump, regardless of the position of the pump in space.